Waste heat is often produced as a byproduct of industrial processes, where heat from flowing streams of high-temperature fluids must be removed.
Typical industrial processes which produce waste heat are gas turbines for mechanical drive as well as power generation applications, gas engines and combustors. These processes typically release exhaust combustion gases into the atmosphere at temperatures considerably higher than the ambient temperature. The exhaust gas contains waste heat that can be usefully exploited, e.g. to produce additional mechanical power in a bottom, low-temperature thermodynamic cycle. The waste heat of the exhaust gas provides thermal energy to the bottom, low-temperature thermodynamic cycle, wherein a fluid performs cyclic thermodynamic transformations, exchanging heat at a lower temperature with the environment.
Waste heat can be converted into useful power by a variety of heat engine systems that employ thermodynamic cycles, such as steam Rankine cycles, organic Rankine or Brayton cycles, CO2 cycles or other power cycles. Rankine, Brayton and similar thermodynamic cycles are typically steam-based processes that recover and utilize waste heat to generate steam/vapor for driving a turbine, a turboexpander or the like. The pressure and thermal energy of the steam or vapor is partly converted into mechanical energy in the turboexpander, turbine or other power-converting machine and finally used to drive load, such as an electric generator, a pump, a compressor or other driven device or machinery.
Conversion of waste heat into useful mechanical power can substantially improve the overall efficiency of the power conversion system, contributing to the reduction of fuel consumption and reducing the environmental impact of the power conversion process.
Therefore, high-efficiency methods and systems for transforming thermal power into useful mechanical or electrical power are desirable.